A nonaqueous electrolyte secondary battery has been developed for use as a high-energy density battery. Such a nonaqueous electrolyte secondary battery is charged/discharged by the migration of lithium ions between the negative electrode and the positive electrode. The nonaqueous electrolyte secondary battery is expected to be utilized also as middle or large power sources besides power sources for miniature electronic devices and is therefore desired to have a higher energy density.
A nonaqueous electrolyte secondary battery comprises a lithium transition metal complex oxide as the positive electrode active material and a carbon material as the negative electrode active material. JP-A 2001-23629(KOKAI) discloses, for example, a nonaqueous electrolyte secondary battery using a lithium-nickel complex oxide having a high energy density as the positive electrode active material. However, this lithium-nickel complex oxide is less thermally stable and there is a problem of lower battery safety.
On the other hand, KOSUGI Shinichiro, and two others, “Toshiba Review”, 2008, vol. 63, No. 2, pp. 54-57, discloses a nonaqueous electrolyte secondary battery using a lithium-titanium complex oxide as the negative electrode active material. The reference discloses that such a battery is resistant to thermorunaway even if internal short circuits are developed by, for example, external force and is therefore improved in safety.